Directive system for wave guide feed to parabolic reflector



July 29, 1952 J. s. FOSTER 2,605,416

' DIRECTIVE SYSTEM FOR WAVE GUIDE FEED TO PARABOLIC REFLECTORS Filed Sept. 19, 1945 FIG. 4

, INVENTOR JOHN STUART FOSTER ATTORNEY SUNI DTJ T Patented July 29, 1952 ES *PAITEV nmEorIvE SYSTEM FOR WAVE GUIDE FEED TQ PARABOLIC REFLECTOR john Stuart Foster, MontreaL'Quebec;. Canada, o assignor, by mesne assignments, to theUniteil f I States of-America as r ta'ry of the Navy epresented by the Secrev I f Al plieationseptember 19, 1945, SerialNo. 617363 My present invention relates todirective radio antennas in general and in particular to antenna means for illuminating a parabolic reflector with energy from a wave guideextending through and alongthe axis of such a reflector.

- Inradio apparatus employing frequencies sufficiently high to permit the use of wave guides for transmission lines and parabolic reflectors as elements in the antenna systems thereof, it is convenient to' construct a directive antenna of a'parabolic reflector or paraboloid having an open ended wave guide transmission Y line mounted in and projecting through a hole at the center and along the axis of such reflector up to, but not quite touching the focal point thereof. Energy emerging from the open end of the waveguide is then reflected to the paraboloid by a small disc mounted on suitable framework near the mouth of the wave guide. The reflecting disc and mouth of the wave guide are usually positioned to include between them the aforementioned focal point.

A chief difficulty with this type of illuminat ing source fora parabolic reflector is that in effect a ring source of illumination is obtained from the reflecting disc rather than a point source and therefore the energy, illuminating the paraboloid cannot be made to come effectively from the focal point thereofn Consequently the beam reflected from the paraboloid will be distorted and contain a relatively large number of side lobes and the gain of the main lobe will be smaller than is'desirable. I

It is therefore an object of my invention to provide illuminating means for a parabolic reflector that will produce a point source of radiamen which may be adjusted substantially to coincide with the focal-point of the parabolic reflector.

.lt is a furtherjobject-of my invention to provide such illuminating mneansthat willbe self supporting.mechanically and .requireno external struts or framework. 1 7

It is a still further object of my invention to provide such illuminating means that will be able to be mounted inthe open mouth or end of a wave guide without interfering with or attenuating'the energy coming from the wave guide.

It is' another object of my invention to providemeansfor supporting in the. neighborhood of the mouth of a wave. guide one or rnore half wave antennaelements which 'means will not interfere with or attenuate en ergy proceeding from or into the waveguide. 1

- s olaims. (o1. 250-s3.e3)

vention will become apparent, upon a careful consideration ofthe following detailed description when taken together withthe accompanying drawing, the figures of which illustrate typical embodiments of my invention.

Fig. 1 1s an isometric viewpartly cut away of a paralooloid illuminating means of my 'invention;

Fig. 2 is a transverse sectionlooking into the plane defined by the lines 11-11 of Fig; 1

Fig. 3 is a transverse section looking into the plane defined by the lines III-III of 'Fig. 1;

Fig. 4 is a cross sectional View partly broken away of antenna of my invention showing an illuminating means of the type illustrated inFigs.

' 1, 2, and 3 'unounted in a parabolic reflector;

e w. o other moss-racin rasqat aass; directed between thezwide sides;

In'Figs. 1, 2, and 3, a rectangular waveguide I has'an openend 2 in which; a Web 30f flat metal is mounted. The web3 is mountedacross the opening 2 and is "disposed"substantially.in the center of that opening. The web" -3 may be .trapezoidally shapedand'have the shorter of its two parallel edges in the opening}. A parasitic antenna. element 4,'which' maybe a half wave element is mounted substantially perpendicularly inthe web 3 amng'tpe inetr the axis A-A' of the wave guide 'l. A disc {which may be circulan-in -shape, is preferably perpendicularly mounted on the longer of the two parallel edges ofthe welo fi. Matching diaphragms 6 are provided in the wave guide] to match the impedanceef the-antenna- 4 and reflector 5 combined t -the wave guide I. These diaphragms 6 introduce a .shuntsusceptance in a known and usualfashion'; 1 I l The apparatus illustrated in Fig 1, 2, and 3 operates to. provide a subst'anfti'ally point sourceof radiation sea point; 1 "between the parasitic antenna element 4 and'the circular-disc reflector 5, as illustrated in gene 3. The operation of t a m si SJiPl W AEThQ ave; guide I is adapted .to. propagate ,electremagrietic waves in m sa ts .,e e ros iq.fielr v c r substantially wholly transverse to the longitudinal axis e O t e W ve g idgg .Such; modem 3 TElmode- JQthq 2 5 s i s e. ilar desirable characteristics may be eiised-if gs' ired When energy inv thef IElm inode-p f soilai fi l' s s mine as gnaw. W111 Re e ie refle t;

v ts'wi l Y 7 of fl r guide in a reqt p perpendicular to the plane oflthe we exer -1 th Parasi ic antenna a 3 disposed perpendicularly to the plane of the web 3, is substantially parallel to the direction of the aforementioned electrostatic field vectors, and will become a parasitic radiator when for example energy emerging from the wave guide I is incident upon it. The antenna element 4 will then re-radiate and some of its energy will be incident upon the nearer surface of the circular disc reflector 5. r This energy will be reflected from the disc 5 and;will meet with other waves coming from the wave guide ,Landhthe,

antenna element 4. Relatively strong radiation will come from the antenna elements inasmuch as this element is substantially a half wave radiator, and therefore, resonant to the energy emerging from the wave guide I. The net effect of the energy being re-radiated from the antenna In Fig. 4 apparatus. like that shown in Figs. 1,

2, and 3 is employed in combination with a parabolic reflector l5 to-produce an antenna having a relatively narrow and highly col-limated beam with high gain in the major lobe'and relatively small side lobes, A'wave guide l0, similar to the wave guide I, of Fig. Lhas an open end l2,'with the edges [3 ofthe upper and lower walls II and l l'respectively cutaway or beveled in the neighborhood of the opening 12. A web 3, antenna element '4, and' refl'ector disc 5, all substantially identical to similarly numbered elements in the apparatus of Fig.1, are provided in the opening I2; The web is mounted across the opening 12 in the narrow. walls 'ofthe wave guide It). Impedance matching diaphragn s '6 substantially identical to similar diaphragms in the apparatus of Fig 1 are also provided. Thewave. guide 10 is mounted in and through the parabolic reflector 15 substantially along the-principal axis B-B thereof. Thus the longitudinal axis of the wave guide 10 and the principal axis of the parabolic reflector l5 are substantially coincident. The electrostatic field vectorE of the energy in the waveguide I0 is directed between the upper wide wall II and the'lower 'wide wall 1'! of the wave guide Ill. The point lfrom which theenergy radiated by the antenna 4 and reflecting disc 5 in combination'appears to be coming is located substantially coincident with the focal point of the reflector l5. Thus energy 16 radiating from this point 1 is directed at the-reflecting surface 18 of the parabolic reflector 1-5 and is reflected from that surface as substantially parallel rays of radiant energy H; Since "the reflected energy will be comprised of substantially'parallelrays l1,

it follows that, the major lobe of theantenna illustrated in Fig. 4 will be relatively narrow, and the gain of this major lobe will be relatively" high.

-I have found that when the point T'Of the 'illu-.

minating means of my invention is 'placedsuba substantially flat metallic'web 'nav ngmstam tenna of Fig. 4 will be-narrow and have highgain of negligibleimportance.

" while the minor lobes will be relatively small and are feasible for the various components of the illuminating means of my invention, I prefer to use certain dimensions, one set of which is hereinbelow set forth merely as an example. Thus referring particularly to..Eigs. 2 and the web 3 extends outwardly from the wave guide I, a distance substantially equal to 0.446 times the free space wave length A of radiation from the wave guide I, the diameter of the reflecting disc 5 is "substantially equal to'. 1.9% and the parasitic antenna'element 4 is placed a distance substantially equal, .to 0.273% inside the nearer surface of the reflectingdisc 5 or correspondingly a distance substantially equal to 0.1737\ from the opening 2 of thewave guide I, and is of a length substantially equal to 0.546%. It is to be borne in mind however that these dimensions are merely exemplary-and in no manner to be considered limiting, as the apparatus of my invention will perform satisfactorily if constructedwith .a variety-of other dimensions.

It is to beunderstood that theweb- 3, need not be trapezoidally-shaped, or have any particular shape, and that the reradiati-ng meansof my invention may comprise one ojrlmore parasitic antenna elements similar to the antenna element 4. Therefore, although I haveshown and described only certain speciflc. embodiments of my invention, it is understood that .the invention is not to be limitedexceptjinsofar as is necessitated by the prior art and spirit. of the appended claims.

l. Electromagnetic wave controlling apparatus comprising, an open ended. wave. guide adapted to propagatev electromagnetic waves, in a mode having its electrostatic field vector polarized in a predetermined direction substantially wholly transverse to the longitudinal axis of said wave guide, a substantially flat metallic web positioned at the open end of said wave guide .in a plane substantially perpendicular to said predetermined direction and projecting outwardly from said end substantially in the direction ofsaid longitudinal axis, and at least one parasitic antenna element substantially perpendicularly disposed in said web.

2. Electromagnetic wave cbntrolling apparatus comprising, an open ended rectangular wave guide adapted to [propagate electromagnetic waves ina mo de having its electrostaticfield, vector polarized a predetermined direction vsubstantially wholly transverse to. the longitudinal axis of said'wave guide, a substantiallyfflat metaldirection and projecting-outwardlyfrom said end substantially inthe direction of said longitudinal axis, and at least one substantially half wave parasitic antenna element substantially 'perpeni dicularly disposed in Sald1Wb;alIl'd extending sub: stantially equal distances there'through.

3. Electromagnetic wave control-ling apparatus comprising, an open ended rectangular wave l guide adapted to propagate electro 'nagne'ti'c; waves of a given wave ilengthin a mode having its electrostatic field vector 'pcl ariz'ediin. ia-prede-v iermined direction ubs a tiall fw l y.transsecond, parallel edges disposed with the first of said parallel edges 'acros's 'th'e op n .endof. said,

wave guide in a plane substantially perpendicular v to said predetermined direction andfplqiecting outwardly from said wave guide substanti'ally'in the direction of said longitudinal axis, a parasitic antenna element having a length substantially one-half of said given wave length and substantially perpendicularly disposed in and substantially equidistantly projecting through said web at a point lying substantially on the linear projection of said longitudinal axis, and a substantially circular and flat metallic disc fixedly disposed on the second of said parallel edges of said web, the respective planes of said web and said disc being substantially mutually perpendicular.

4. The apparatus of claim 3 in which said web extends outwardly from said wave guide a distance substantially equal to 0.446)\, said parasitic antenna element is disposed outwardly from said wave guide a distance substantially equal to 0.173% and is substantially 0.54m long, and said disc is of a diameter substantially equal to 1.97, where A is the free space wave length of energy at the operative frequency for said apparatus.

5. A directive radio antenna comprising, a parabolic reflector having a centrally disposed hole therein, an elongated open ended wave guide fixedly mounted in said reflector through said hole and extending into said reflector substantially along the axis thereof toward but not reaching the focal point thereof, said wave guide being adapted to propagate electromagnetic Waves in a mode having its electrostatic field vector polarized in a predetermined direction substantially wholly transverse to said longitudinal axis, a substantially flat metallic web disposed at the open end of said wave guide in a plane substantially perpendicular to said predetermineddirection and extending outwardly from said end in the direction of said axis through said focal point, a parasitic antenna element disposed substantially perpendicularly in said web, and a substantially flat metallic reflector disc fixedly mounted on the outer edge of said web substantially perpendicular to said axis, the center of radiation of said parasitic element and reflector disc being substantially coincident with said focal point.

6. Electromagnetic wave controlling apparatus comprising an open-ended rectangular wave guide adapted to propagate electromagnetic waves of a given wave length in a mode having its electrostatic field vector polarized in a direction substantially wholly transverse to the longitudinal axis of said wave guide and substantially wholly transverse to a pair of parallel sides of said wave guide, a substantially flat metallic web positioned at the open end of said Wave guide in a plane parallel to and equidistant from said pair of sides, said web projecting outwardly from said open end in the direction of said longitudinal axis, a parasitic antenna element disposed in said web substantially perpendicular to said web, said antenna element extending substantially equal distances through said web and having a length substantially one-half of said given wave length of said electromagnetic waves and a substantially flat metallic reflector disc fixedly mounted on the outer edge of said web and subextending into said reflector through said hole jecting outwardly from said open end in the direction of said longitudinal axis, a parasitic antenna element disposed in said web substantially perpendicular to said web, said antenna element extending substantially equal distances through said web and having a length substantially one-half said given wave length of said electromagnetic waves, a substantially flat metallic reflector disc fixedly mounted on the outer edge of said web substantially perpendicular to the longitudinal axis of said guide, and a parabolic reflectorformed with a centrally disposed hole therein, said wave guide being fixedly mounted in said reflector through said hole and along the axis of said reflector, the center of radiation of said parasitic element and reflector disc being substantially coincident with the focal point of said parabolic reflector.

' 8. Electromagnetic wave controlling apparatus comprising an open-ended wave guide adapted to propagate electromagnetic waves in a mode having its electrostatic field vector polarized in r a direction wholly transverse to a predetermined plane coincident with the longitudinal axis of said guide,'a substantially flat metallic web positioned at the open end of said guide and substantially parallel to said predetermined plane, said web I having a thickness small compared tothe crosssectional dimensions of said wave guide, at least one parasitic antenna element disposed in said web perpendicular to said web and a substantially flat metallic reflector disc fixedly mounted on the outer edge of said web and perpendicular to said longitudinal axis.

, JOHN STUART FOSTER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,206,923 Southworth July 9, 1940 2,234,293 Usselman Mar. 11, 1941 2,422,184 Cutler June 17, 1947 2,429,640 Mieher "Oct. 28, 1947 2,441,574 Jaynes May 18, 1948 2,446,436 Rouault Aug. 3, 1948 2,465,673 Breen Mar. 29-, 1949 2,491,493 Goldberg Dec. 20, 1949 

